b.wordtothewise.com has no MX records.
Question and response
Question
dig b.wordtothewise.com. MX
Answer
The response has no answer records.
Authority
wordtothewise.com. 86400 SOA b.wordtothewise.com. hostmaster.wordtothewise.com. 2015102961 14400 3600 2592000 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0